One zone or two zones in the room of fire origin during fires? The effects of the air-handling system

A two-zone model, CFAST, has been widely used in the fire research community. However, this study indicates that the CFAST model generally overpredicts the upper layer temperatures in the burn room because the zonal assumption is likely to break down in the burn room. It was found that the room-averaged temperatures obtained from the CFAST model were in good agreement with the experimental results (one zone assumption in the burn room). The prediction of CO concentration is inconsistent. The CFAST model tends to overestimate CO concentration when the air-handling system is in operation, and to underestimate CO when the system is off.